1. Technical Field
The invention relates to methods and devices to facilitate bi-directional blood flow through a single access point. More particularly the invention relates to extracorporeal hemodialysis of a patient's blood with a single cannulation even in patients having difficult sites to access.
2. Description of the Related Art
Historically, kidney diseases have been of critical concern to human life. Many kinds of kidney diseases interfere with the function of the kidney such that the kidney ceases to remove waste and excess water from the blood. When the kidney is sufficiently impaired that large portions of the waste products and water are not removed from the blood, the life of the patient cannot be preserved unless a way is provided for artificially performing the function of the impaired kidney. Even today, the same general procedure is used for dialyzing patients' blood that was used very early in the treatment of kidney disease.
For example, the most commonly accepted practice for dialyzing a patient's blood extracorporeally requires the surgical creation of a vascular access such as arterio-venous fistula (artificial connection between artery and using the native vein) or graft. Grafts are much like fistulas in most respects, except that an artificial vessel is used to join the artery and vein. The graft usually is made of a synthetic material, often PTFE, but sometimes chemically treated, sterilized veins from animals are used. Grafts are inserted when the patient's native vasculature does not permit a fistula.
Sufficient blood flow for dialysis is then obtainable by cannulation of fistula or graft with large bore needles. Normally, two hollow needles are used to perform two cannulation on the patient hemodialysis access (fistula or graft) so that two point blood-communication sites exist simultaneously in the patient. Conventionally, blood is withdrawn from one part of the punctured hemodialysis access, forced through a hemodialyzer and thereafter forced into the remaining part of the hemodialysis access. The needles have to be substantially distant from one another to prevent recirculation of blood between the access sites.
It is well-known that the life expectation and effective function of a hemodialysis access is inversely related to the number of cannulations. Tissue repeatedly subjected to the trauma of cannulation is much more susceptible to inflammation and neointimal hyperplasia, thrombosis and pseudo aneurism development. Such trauma may result in destruction of the graft or fistula triggering a requirement for another expensive operating procedure to replace the graft or fistula so that routine treatment may be resumed.
Systems for hemodialysis access to a fistula or graft cannulation can generally be divided on the following groups.
Two Needle Cannulation
Two needle cannulation procedures are well known being the first developed and the most widely used s at the present time. They are able to provide flow high flow rates of up to 600 ml/minute to minimize patient clinical procedure time and provide the best nitrogen and creatinine clearance/removal from the body. The disadvantages of these systems compared to a single cannulation approach, include pain and trauma to access, the risk for developing complications including pseudoaneurysm, prolonged post treatment bleeding, outflow stenosis and the presence of matured vascular access. In addition, the preferred placing of two needles at least 12 mm apart from each other which cannot be achieved at least at 30% of all newly placed accesses (so called failure or non-maturation of vascular access), An example of two needle cannulation can be found at the website of Baxter.
Sequential Flow Single Needle Cannulation
A sequential flow single needle cannulation system uses a single needle cannulation for both removing and replacing blood by alternating between forward and reverse flow through the single needle. The benefits of this system are that the one needle cannulation decreases trauma and pain in the area of the cannulation since only one cannulation is required. A disadvantage is that the high recirculation rate results in extensive remixing of treated and untreated blood, which reduces the effectiveness of the dialysis procedure. An example of this approach is disclosed in U.S. Pat. No. 4,940,455.
Telescoping One Needle Cannulation
Another single needle system including a one needle cannulation uses dual coaxial tubes to form an integral 2 lumen needle to simultaneously add and remove a patient's blood with one introduction point. The benefit of this system is that only one needle cannulation is required thereby decreasing the trauma/pain in the area of cannulation. The disadvantages of this procedure include that using a large sized (usually 14 gauge) cannulation needle as an outer tube (without using a single or double dilator) which restricts blood flow through the system to an average flow of 300-400 ml/minute. These low flow rates are not acceptable for the most hemodialysis patients and not preferred by the care providers. Furthermore, using a rigid inner tube material makes the device inappropriate to use in difficult geometry access such as stenotic, snail, torturous and angled fistula. An example of this system is the OneSite® system from NxStage® Medical, Inc.